The present invention relates to intumescent compositions and, more particularly, to an aqueous-based intumescent solution which is useful in extinguishing fires that can be used as a liquid fire-extinguishing medium in a fire extinguisher.
Aqueous-based intumescent compositions have been used to protect flammable surfaces from heat and flame. The function of these compositions has been primarily insulative. The compositions have not been used to extinguish an already burning fire. Rather, the coatings have been applied to substrates, such as wall board, and dried, such that in the event of fire or intense heat flux the coatings react and generate a foam having a high char value which insulates the substrate and prevents it from burning.
One aqueous-based intumescent composition that has been used to form protective flame-proof coatings is described in U.S. Pat. No. 3,955,987 to Schaar et al. That composition is a film forming composition and contains a polyol, a phosphate source, and a gas-generating agent and produces a flame-resistant polymeric foam upon heating. Typical examples of the phosphate sources disclosed in the Schaar et al patent are monoammonium phosphate, diammonium phosphate and an ammonium polyphosphate sold by Monsanto Company under the trademark PHOSCHECK P/30. In certain embodiments, coatings containing one or more of these phosphate sources, sucrose, cyanoguanidine, titanium dioxide and a polymeric film former react to produce a flame-resistant polymeric foam which protects the underlying substrate upon exposure to flames. Kasten, U.S. Pat. No. 4,247,435 discloses a related class of intumescent coatings containing a chelating agent to impact viscosity stability to the composition, i.e., to prevent viscosity from increasing over time.
Previous aqueous-based intumescent compositions and particularly the compositions described in the Schaar et al patent are not true solutions and, consequently, are not desirable for use in fire extinguishers. The intumescent compositions described in the Schaar et al patent are thixotropic supersaturated suspensions containing insoluble components that tend to settle out over short periods of time. Consequently, they cannot be readily dispensed by pumping and they are not useful as the fire extinguishing medium in fire extinguishers. To be useful in fire extinguishers, intumescent compositions must be capable of coating a burning object, intumescing and generating a fire-resistant foam which shuts off the air supply to the burning object. There is no indication in Schaar et al or the prior art that this function can be achieved within the compositional restraints of a true solution. To the contrary, prior art compositions are designed to be applied as a permanent or temporary intumescent paint in advance of a fire. On the other hand, an aqueous intumescent solution would be a very desirable fire extinguishing medium because it would be storage stable, readily pumpable, and the water itself would help extinguish the fire.
Thus, there is a need for an intumescent aqueous solution that is useful in extinguishing fires.